Apparatus for interiorly coating lamp exhaust tubes



April 29, 1958 J. A. BILLSON ET AL 2,832,309

APPARATUS FOR INTERIORLY COATING LAMP EXHAUST TUBES Filed Nov. 25. 1956 3 Sheets-Sheet l 9 John B. S kevenson,

April 29, 1958 J. A. BILLSON in AL 2,832,309

APPARATUS FOR INTERIORLY COATING LAMP EXHAUST TUBES Filed Nov; 2a. 1956 3 Sheets-Sheet 2 lnvan tor's: John A. BiLLson, W John B. Sfitevenson Then A lr tow'neg.

April 29, 1953 J. A. BILLSON ETAL 2,832,309

APPARATUS FOR INTERIORLY COATING LAMP EXHAUST TUBES Filed NOV. 23, 1956 3 Sheets-Sheet 3 2a UNLOAD/NG ZOAD/NG 5V0 BRUSH/N6 lnvervtovs John A.BiLLson, John B. Stevensom nited States Patent APPARATUS FOR INTERIORLY COATING LAMP EXHAUST TUBES John A. Billson, Willoughhy, and John B. Stevenson, Euclid, Ohio, assignors to General Electric Company, a corporation of New York Application November 23, 1956, Serial No. 623,941

7 Claims. (Cl. 118-56) This invention relates to apparatus for applying a coating of powdered material to the inner wall of a tubular member such as the glass exhaust tubes used in electric incandescent lamps and similar devices.

In the manufacture of electric incandescent lamps and similar devices it is customary practice to evacuate the lamp envelope or bulb through a glass exhaust tube which is sealed at one end either into the stem tube or the bulb neck of the lamp. In accordance with a recently developed lamp manufacturing technique as disclosed and claimed in co-pending application Serial No. 549,424, R. Malm et al., filed November 28, 1955 and assigned to the assignee of the present invention, the passageway through the exhaust tube is maintained open, during the sealing of the tube into the stem tube or bulb neck and the pinching thereof to form the stem press, by the provision of an internal coating on the exhaust tube of a material suitable for the purpose, such as powdered zirconium oxide, for example. This internal coating on the exhaust tube need be provided only throughout that end portion of the exhaust tube which is to be sealed into the bulb neck or stem tube of the lamp, and for best results should be of uniform thickness throughout and free of voids or bare spots. In addition, such coatings on the exhaust tube should be firmly adherent thereto so as not to flake off the exhaust tubes during the shipment and handling thereof prior to their sealing into the stem tube or bulb neck, as well as subsequent to the sealing of the tubes into the stem tube or bulb neck such as to cause contamination of the finished lamp. It is preferable, also, that the outer side as Well as the end extremity or edge of the exhaust tube be devoid of the coating material so as not to contaminate the fused glass seal between the glass exhaust tube and the glass of the surrounding stem tube or bulb neck.

It is one object of our invention, therefore, to provide automatically operating apparatus for producing firmlyadherent and uniform coatings of powdered material on the inner walls of tubular members of small diameter, such as lamp exhaust tubes and the like, and ata high rate of production.

Another object of our invention is to provide automatically operating apparatus for producing internal coatings of the character referred to on lamp exhaust tubes and the like for a predetermined length inwardly from one end of the tube, with the outer side and end extremity of the tube devoid of such coating material.

Still another object of our invention is to provide apparatus for producing firmly adherent and uniform internal coatings on lamp exhaust tubes for a predetermined distance inwardly from one end thereof and at a high rate of production while maintaining high coating quality.

Briefly stated, in accordance with one aspect of the invention, the lamp exhaust tubes to be coated are placed in holder means which are located around the periphery of a turret mounted for rotation about an axis tilted at an angle of the order of 45 to the vertical, and which are adapted to hold the tubes in a position tilted radially inward of the turret at an angle to its axis approximately corresponding to the angle of tilt thereof so as to position the tubes approximately vertically when carried to the lowermost point in their path of travel around the turret, at which time the lower ends of the tubes are carried through and are submerged to a predetermined level in a suspension or slurry of the coating material to be applied to the tubes. The coated tubes are subsequently carried by the holders on the turret through a heating zone Where the coated ends of the tubes are heated to a temperature suificient to burn out the binder in the coating material and sinter it in place onto the walls of the tubes.

In accordance with a further aspect of the invention, coating removal means are provided adjacent the path of travel of the coated tubes on the turret for cleaning or removing the coating fromthe outer side and the lower end extremity of the tubes during their travel around the machine, the said coating removal means preferably comprising means for directing heated air against the freshly coated outer sides and lower end extremities of the tubes as well as through the tubes so as to dry the coating slurry thereon, and brush means for then engaging and brushing the dried coating off the outer sides and lower end extremities of the tubes.

In accordance with a still further aspect of the invention, the tube holder means on the turret is comprised of a plurality of radially extending tube-receiving grooves which are of semi-circular cross-section corresponding to the tubes and are formed in a bevelled upper periphery of the turret, the grooves being provided with respective suc' tion ports which are continuously connected to a vacuum so as to hold the exhaust tubes in place within the grooves 4 at all times during their travel around the turret.

Further objects and advantages of our invention will appear from the following detailed description of a species thereof and from the accompanying drawings.

in the drawings,

Fig. 1 is a side elevation, partly in section, of a tube coating apparatus according to our invention.

Fig. 2 is a sectional view, on the line 2--2 of Fig. l, of the turret portion of the apparatus with portions thereof shown broken away to more clearly illustrate the internal construction of the turret.

Fig. 3 is an elevation, partly in section, of the tubefeeding means of the apparatus.

Figs. 4 to 8 are views illustrating the successive opera tions which are performed by the apparatus and which comprise, respectively, the end glazing of the tube, the application of the coating material to the tube end, the brushing of the coating material off the outer side and the end extremity of the tube, and the baking of the coating onto the tube.

Fig. 9 is a perspective view of the coatingapplicating means of the apparatus.

Fig. 10 is a plan view, partly in section, of the forced 'air drying means of the apparatus for drying the coating on the tubes, and

Fig. 11 is a perspective view of the brushing mechanism of the apparatus for brushing the coating off the outer side of the tubes.

Referring to the drawings, the tube-coating apparatus according to the invention comprises a turret 1 which is rotatively mounted on an inclined stationary hollow shaft or column 2, by means of spaced roller bearings 3 and 4, so as to be located in a tilted position, as shown. The turret-supporting shaft 2 is fixedly mounted in a sleeve portion 5 of a support bracket 6 upstanding from a stationary or table portion '7 of the apparatus. The turret is rotated at a continuous and relatively slow speed, for example, at approximately one-half revolution per minute, by means of an electric motor 8 mounted on the support bracket 6 and provided with a unitary speed reducer 9 the output shaft 10 of which extends upwardly in parallel relation to the turret support shaft 2 and carries at its upper end a pinion or spur gear 11 meshed with a bull or ring gear 12 fastened to the underside of the turret 1 in concentric relation therewith.

The lamp exhaust tubes or other tubular articles 13 to be coated are supported in place on the turret 1 around the periphery thereof by suitable tube holder means 14 spaced around the periphery of the turret and arranged to hold the tubes thereon in positions tilted radially inward of the turret at an angle to its axis of rotation approximately corresponding to the angle of tilt thereof from the vertical so as to position the tubes approximately vertical when they are located at the lowermost point in their path of travel around the turret. As shown, the said tube holder means 14 preferably comprise a series (144 in the particular case illustrated) of tube-receiving grooves 15 which are formed in a beveled upper peripheral surface 16 on the turret and extend radially thereof. The beveled periphery 16 and the tubeholding grooves 15 therein are inclined radially inward of the turret at an angle to its axis approximately corresponding to the angle of tilt thereof from the vertical so as to position the tubes 13 approximately vertical when located at the lowermost point in their path of travel around the turret. In the preferred form of our coating apparatus, the turret 1 is mounted with its axis of rotation approximately at a 45 angle to the vertical and the beveled periphery of the turret is inclined radish 1y inward thereof at an angle of approximately 45 to the turret axis. With such a construction, the exhaust tubes 13, when positioned in place in the grooves 15 on the turret, are then located in a vertical or nearly vertical position during the course of their travel through the region at the lower side of the tilted turret, and in a horizontal or nearly horizontal position during the course of their travel at the upper side of the tilted turret. The tube-receiving grooves 15 are of semi-circular crosssectional shape, conforming approximately to the circular cross section of the exhaust tubes 13 to be coated, so as to provide a close fit around the tubes when the latter are placed in the grooves.

The tubes 13 are held in place in the tube-receiving grooves 15 on the turret by means of a suction created within each of the grooves. To this end, each tubereceiving groove 15 is provided with a suction port 17 formed in the periphery of the turret 1 within the respective groove. In the particular case shown, each of the suction ports 17 is in the form of a narrow slot formed in the wall of the respective groove and connected by a small passageway or aperture 18 in the turret wall to one of a group (four in the particular case illustrated) of arcuate vacuum-supply manifold chambers 19 provided in the turret. The apertures 18 are of such a restricted size (for example, around .040 diameter in the particular case illustrated) as to prevent sufiicient air leak into the manifold chambers 19, when tubes 13 accidentally fall offgor'are not present in all the tubereceiving grooves 15, to reduce the vacuum in the chambers to the point where the other tubes 13 remaining on the turret will slide down or fall off the turret. In this connection, the extreme case is when the machine is started at the beginning of a work run, at which time the turret 1 is entirely empty of tubes 13 except for the first tube 13 that has been placed in one of the tubereceiving grooves 15 of the turret. Even in this extreme case, however, there is sufficient vacuum in each of the manifold chambers 19 to hold the tubes 13 in place in the grooves 15 as they are placed therein.

During the operation of the apparatus, a vacuum is continuously supplied to each of the vacuum manifold chambers 19 and through the passageways E8 to the port 17 of each individual tube-receiving groove 15' through rotary valve means 20 comprising a ring-shaped eta-- of the stationary member 21 and spring collars 25 fixedly secured on respective spring posts 26 secured to and extending from a cross arm 27 which is fixedly secured on the upper end of the turret support shaft 2. The spring posts 26 extend through the coil springs 24, and at least one of the said posts fits into an opening 28 in the stationary upper valve member 21 to lock the said member 2i against rotation along with the turret about the turret shaft The stationary valve member 21 is provided with a plurality of arcuate vacuum supply channelways or slots 29 in its under face 22 which extend in a spiral manner about the turret axis so as to successively overlap one another at their opposite ends. The vacuum supply channelways 29 communicate with one or the other of a plurality (four) of vacuum ports 3i) in the upper face 23 of the turret, which ports 30 in turn communicate with respective ones of the vacuum supply manifold chambers 19. The turret 1 is additionally provided with shallow cross slots 31 in its upper face 23 which extend radially inward of the turret from the ports 3d therein so as to maintain the supply of vacuum to the said ports from the spiral channelways 29 at all times during the rotational movement of the turret, and particularly during those time intervals when the vacuum :ports 30 are traversing the region of the overlapping ends of the spiral channelways 29. Vacuum is supplied to the spiral channelways 29 of the stationary member 21 of the rotary valve 2a through the hollow interior of the turret sh aft 2 the lower end of which is connected by a conduit 32 to a source of vacuum of suitable degree, for example of the order of 21 to 25 inches of mercury, and the upper end of which is provided with a connector block 33 having a plurality of outlet connection nipples 34 (four in the particular case illustrated) which are connected, by respective conduits 35 and nipples 36, to respective ones of the spiral channelways 29 in the stationary valve member 21.

'In the operation of the tubercoating apparatus according to the invention, the exhaust tubes 13 to be coated are placed in the successive tube-receiving grooves 15 on the turretat a loading position which, as shown in Fig. 2, is preferably located a short distance around the turret, c. g., an arcuate angle of'45" or so beyond, the upper side of the turret which is the unloading position of the apparatus. For the sake of simplicity of illustration, however, the loading of the tubes 13 onto the turret 1 is illustrated in Fig. l as taking place at the upper side of the tilted turret. As shown in Fig. 1, the tubes 13 are placed in the tube-receiving grooves 15 on the turret in a position such that the lower end portion of the tubes extend outwardly beyond the periphery of the turret so as to be freely accessible for subsequent coating. The tubes 13 to be coated may be loaded into the tube-receiving grooves 15 of the turret either manually or by means of suitable automatic tube-loading means such as illustrated at 37 in Figs. 1 and 3.

The particular tube-loading means 37 illustrated comprises a tube storage hopper 38 mounted adjacent and above the beveled periphery 16 of the turret and in which a supply of the tubes 13 are stored in side-by-side relation in a position parallel to the position in which the tubes are to be delivered to and held in the tubereceiving grooves 15 of the turret at the tubedoading posi tion. The hopper 38 is provided with a slotted sloping bottom wall 39 and an oppositely sloped side wall 40 joined at its lower end with a guide wall 41 which closely overlies the bottom wall 39 for some distance upwardly from its lower end to form therewith a confined discharge passageway 42 through which the tubes 13 can roll down only one at a time (i. e. in single file) to a discharge opening i3 at the lower end of the hopper where the tubes then drop out into successive tube-receiving grooves 15 on the advancing turret. The lower end of the hopper in which the discharge opening 43 is located is spaced from the beveled periphery 16 of the turret a distance slightly less than the diameter of the tubes 13 so that the latter will drop only into the grooves 15 on the turret, and only one at a time thereinto, as the grooves pass underneath the discharge opening 43 of the hopper To facilitate the continued gravity feed of the exhaust tubes 13 from the pile thereof in the storage hopper 38 into the confined discharge passageway 42 thereof, a pivoted agitator blade or finger 44 is provided within the hopper for agitating the pile of exhaust tubes 13 in the hopper at a region adjacent the entrance to the confined discharge passageway 42. The agitator blade 44 is fixedly secured on a shaft 45 which is rotatably mounted on the hopper 38 and is intermittently oscillated to swing or rock the agitator blade 44 back and forth so as to introduce a tongue 4'6 on the lower end of the agitator blade through an opening 47 at the lower end of the inclined side wall 4i"! of. the'hopper and into the pile of exhaust tubes t3 ad jacent the entrance to the confined discharge passageway 42 of the hopper. The agitator blade shaft 45 is so tatably mounted in a bracket 48 fastened to the hopper side wall 49 and it is intermittently oscillated, to swing or rock the agitator blade 44 back and forth, by means of a spring-loaded actuating arm 50 the upper end of which is fastened to the shaft 45 and the lower end of which intermittently engages with striker pins 51, on a pin wheel 52 fastened on and rotating with the turret drive shaft 10, to cause theactuating arm 50 to swing and thus rotate the agitator blade shaft 55 in a direction to introduce the tongue 46 on the actuator blade into the pile of exhaust tubes 13 in the hopper 38. The actuating lever50 and the associated agitator blade 44 are swung back in the opposite direction to their retracted position, each time the lower end of the actuating lever rides off and disengages one of the striker pins 51 on the rotating pin wheel 52, by the force of a tension coil. spring 53 which is connected between spring posts 54 and 55 on the actuating lever 50 and hopper 38, respectively. The retracted position of the actuating lever 50 is determined by the engagement thereof with a limiting stop 56 on the hopper 38.

After being loaded into the tube-receiving grooves 15 on the turret 1, the exhaust tubes 13 are then carried by the turret through a glazing zone (as indicated in Fig. 2) located a short distance before the tubes reach the lowermost side of the turret, where the upper ends of the tubes 13 pass beneath and are heated by gas fires 57 (Fig. 4) from a gas burner 58, mounted above the turret periphery 16, to thereby fire polish the said ends of the tubes 13. These fire-polished ends of the exhaust tubes 13 are the ends which, when the tubes are subsequently sealed into a lamp stem press, will form the outer ends of the lamp exhaust tribulation and which will therefore be inserted into the compression rubber chuck of the conventional lamp exhaust machine during the lamp exhausting operation. The tire-polishing of these exhaust tube ends therefore eliminates the presence of any sharp glass edges at the outer ends of the lamp exhaust tribulations such as would be likely to cut and damage the rubber compression chuck of the lamp exhaust machine during the insertion of the lamp exhaust tubulation thereinto.

Following the glazing of the upper ends of the exhaust tubes 13, the tubes are carried by the turret to, and are advanced through,v a coating zone located at the lowermost side of the turret as indicated in Fig. 2, where the exposed lower end portions of the tubes are carried into and immersed to a predetermined level in a suspension or slurry 59 (Fig. 5) of the coating material to be applied to the tubes to thereby cause the deposition of a layer of 6 the coating suspension on the lower end portions of the exhaust tubes 13, on both the outer and inner walls thereof, for a predetermined distance inwardly of the tubes from their lower ends. ends of the exhaust tubes 13 during their travel through the coating Zone is preferably performed by suitable coating means 60 located at the lowermost side of the turret 1. The particular coating means 60 illustrated comprises a vertically movable dip tank in the form of a troughshaped dipper 61 carried at the lower end of a vertically reciprocablc support rod 62 depending from a slide 63 which is mounted for vertical sliding movement in a guideway 64- formed in a guide block 65 fastened to a support bracket 66 upstanding from the machine table 7. The slide 63 and the associated support rod 62 and dipper 61 are reciprocated to intermittently submerge the dipper 61 in a reservoir 67 of the coating suspension carried in a large supply tank 68 mounted on the machine table 7 beneath the lower side of the turret periphery 16, the periodic submerging of the dipper in the coating suspension reservoir 67 not only serving to refill and main.- tain the coating suspension in the dipper 61 at a constant level therein at all times so as to insure the coating of the tubes 13 uniformly up to a predetermined level from their lower ends, but also serving to periodically agitate the coating suspension reservoir 67 in the supply tank 68 so as to continually maintain the coating particles uniformly dispersed in the suspension. The intermittent vertical reciprocation of the slide 63 to submerge the dipper 61 in the coating suspension reservoir 67 is effected by a crank mechanism 69 comprising a motor-driven pulley 70 rotatably mounted on the guide block 65 and provided with an eccentric pin 71 connected to one end of a link '72 the other end of which is connected to the slide 63. The pulley 70 is rotated at a constant speed suificient to submerge the dip tank or dipper 61 two or three times during the travel of each exhaust tube 13 through the coating zone, by means of a belt 73 running around the pulley 70 and around a drive pulley 74 mounted on the output shaft (not shown) of a combina tion electric motor and speed reducer unit 75 mounted on the support bracket 66. As shown in Fig. 9, the trough-shaped dip tank or dipper 61 is slightly bowed in the horizontal plane, as by being formed into a shallow V-shape, to more or less conform to the arcuate path of travel of the lower ends of the exhaust tubes 13 during their travel through the coating zone. Also, to reduce the rate of evaporation of the volatile constituents of the coating slurry in the dipper 61 and supply tank 68, the latter is provided with a removable cover 76 having a narrow arcuate slot 76 through which the tubes 13 are introduced and pass during their travel through the coating zone.

The coating suspension 59 employed may be any of the compositions referred to in co-pending application Serial No. 549,424, Malm et al., filed November 28, 1955 and assigned to the assignee of the present invention and comprising, in general, a powdered material suspended in a suitable vehicle to form a slurry of suitable viscosity. Thus, as disclosed in the aforesaid Malm et al. application, the coating suspension 29 may consist of powdered magnesium oxide suspended in a suitable denatured alcohol, such as that commercially known as Synosol, in the proportions of, for example, from to 250 grams of magnesium oxide per 1000 ml. of alcohol. To reduce and delay the thickening of this slurry, a small amount of acetic acid may be added to the suspension in the range of, for example, a few drops to one or two ml. per 100 ml. of suspension. Further improvement in this respect is obtained by the addition of a small amount of a suitable sequestering agent such as ethylene diamine tetraacetic acid (commonly known as EDTA) for sequestering the free ions present in the suspension and rendering them inactive. Thus, an addition of from /2 to 1 ml. of

a 5% solution of ammonium salt of EDTA to 100 ml. of

The coating of the lower properties.

a the suspension has been found satisfactory for this purpose. To improve the adherence of the powdered magnesium oxide coating to the walls of the exhaust tubes, and at the same time improve the uniformity of the coatings on the exhaust tubes, a small amount of a suitable binding agent such as ethyl borate may also be added to the suspension. Thus, from 1 to 5 ml. of ethyl borate per 100 ml. of the magnesium oxide suspension will afford the above mentioned improvement.

As disclosed in the previously mentioned Malm et al. application Serial No. 549,424, the coating material preferably employed consists of a suspension of powdered zirconium oxide in a suitable vehicle preferably comprising water and a small addition of a suitable binder such as polymerized (i. e. a co-polymer of) vinyl. methyl ether and maleic anhydride commonly known as PVM/MA. The polymerized viny methyl ether and maleic anhydride is used to increase the viscosity of the zirconium oxide slurry, to improve the suspension of the zirconium oxide particles (it acts partially as a dispersing agent), and to give good and consistent coatings on the exhaust tubes. Preferably, in addition, small amounts of ammonium hydroxide and boric oxide are also incorporated in the zirconium oxide slurry. The ammonium hydroxide addition is employed to control the pH of the slurry and thus control its viscosity. The boric oxide addition to the suspension is employed as a fusing or sintering agent to obtain improved adherence of the zirconium oxide powder particles to the wall of the exhaust tube after the binder is burned off. Without boric oxide in the zirconium oxide coating slurry, the zirconium oxide tends to flake off the wall of the exhaust passageway in the stem press of the finished lamp. While loose zirconium oxide powder in the lamp envelope is not deterimental to lamp quality, nevertheless the presence of such loose powder within the lamp envelope is more or less undesirable from an appearance standpoint.

As a specific example, a suitable zirconium oxide slurry 59 for application to the walls of exhaust tubes 13 may be prepared by milling for an extended period, preferably from 24 to 48 hours or so, a mixture of the following general composition:

Zirconium oxide grams 1200 Water ml 800 Polymerized vinyl methyl ether and maleic anhydride ml Ammonium hydroxide ml 40 Boric oxide ml 18 After milling of the above ingredients, the milled suspension is washed out of the milling container with 400 ml. of water containing 4 ml. of a suitable wetting agent such as that commercially known as TGEPAL 530, which is a polyoxyethylated nonylphenol of such ethylene oxide and nonylphenol balance as to give medium hydrophobic qualities. It is a surface modifying agent used to give coatings free of pin holes and other coating defects, and it is manufactured by the Antara Chemical Division of the General Aniline and Film Corporation. The resulting milled zirconium oxide slurry has excellent keeping For example, even after an extended period of three months or so it does not exhibit any deterioration or gelling. Shortly before use of this zirconium oxide slurry to coat exhaust tubes (preferably not more than 12 hours or so before use), 10 ml. of ethyl borate is added to each 300 grams of the slurry. This ethyl borate addition improves the coating characteristics of the slurry when applied to the exhaust tubes. Inasmuch as the keeping quality of the coating slurry after the addition of ethyl borate is relatively poor, the slurry with the ethyl borate addition should be used within a relatively short period of not more than 24 hours or so.

Following the application of the layer of coating suspension to the inner and outer walls of the exhaust tubes 13 to a predetermined height from their lower ends by the coating means 50, during the travel of the tubes 13 through the coating zone, the coated tubes 13 are then carried by the turret 1 through an air-drying zone as indicated in Fig. 2 where the wet coating material on both the inner and outer sides of the tubes is dried, by directing heated air against the coated outside portion of the tubes as well as down through the tubes from the top thereof, to thereby evaporate the water or other suspending vehicle in the layer of coating material on the tubes. As shown in ll), the heated air is directed against the coated onto des or lower ends of the tubes and down through the coated tubes by means of a pair of hot air supply manifolds or pipes 77 and 78, respectively, which are arcuate shaped and are mounted to extend adjacent and along the path of travel of the tubes 13, respectively in overlying relation to the coated lower ends of the tubes and opposite the open upper ends thereof. The manifold pipes 77 and 78 are mounted on one or more support arms 79 fastened on a support bracket St upstanding from the machine table 7, and they are provided with a series of nozzle openings or orifices 31 and 82 along the length thereof for respectively directing the heated air introduced into the manifold pipes downwardly against the upper outer side of the coated lower end portions of the tubes, and into the open upper ends of the tubes, continuously during their travel through the drying zone. gated bafiie $3 fastened on the support arm '79 in a position underneath the coated lower end portions of the tubes 13 and coextensive with their path of travel through the air-drying zone, deflects the heated air stream from the lower manifold pipe 77 back up against the underside of the tubes 13 so as to dry the layer of coating material on the undersides of the advancing tubes. The air supplied to the manifold pipes 77 and 78 is heated in a cartridge type electric heater 84 the inlet $5 of which is connected to a suitable source of relatively low pressure compressed air and the outlet 86 of which is connected by branch pipes 87 and 88 to the manifold pipes 77 and 73, respectively.

After the air-drying of the coating material on the exhaust tubes 13, the turret 1 carries the tubes successively through an end brushing zone and a side brushing zone, as indicated in Fig. 2, where the dried coating is cleaned and removed from the lower ends of the tubes and from the outer sides of the tubes by means of a pair of revolving brushes 89 and 90, respectively, as shown in Figs. 6, 7 and 11. The brushes 89 and 90 are rotatably mounted on respective support brackets 91 and 92 fastened on the machine frame 7. The brushes 89 and 90 are rotated or belt-driven by slow-speed electric motors (not shown) which are mounted on the respective brush support brackets 91 and 92 and which drive the brushes by means of belts 93 and 94 running around respective sets of pulleys 95 and 96 mounted on the motor shafts 97 and brush shafts 98.

During the travel across each of the revolving brushes 89 and 9 8, the coated tubes 13 are rotated to insure the thorough cleaning of the coating material from the ends and outer sides of the tubes around their entire periphery.

To this end, the tubes 13, during the course of their travel across each of the brushes 89 and 90, ride against and across soft rubber shoes or insert pads 99 and 1% fixed in stationary spring-loaded holders 101 and 102 mounted on the respective brush support brackets 91 and 92. The engagement of the tubes 13 with the stationary soft rubber shoes 99 and 100, during the travel of the tubes across the revolving brushes 89 and 99, causes the tubes 13 to rotate in their positioning grooves 15 in the turret 1. The shoes 99 and of the tube-rotating means are yieldingly pressed against the advancing tubes 13 on the turret 1 by the force of compression coil springs 103 and 104 which are compressed between the respective shoe holders 101 and 102 and the brush support brackets 91, 92. During their travel across the tube end cleaning brush 89, the tubes 13 are held down in engage- An elonv ment with the said brush by a hold-down stop 105 which overlies and engages with the upperends of the tubes 13 and is supported in place by a bracket 106 fastened to the brush holder bracket 91.

Following the brushing and removal of the coating material from the lower end and outer sides of the tubes 13 by the revolving brushes 89 and 90, the tubes are then carried by the turret 1 through a heating or sintering zone as indicated in Fig. 2 where the lower end portions of the tubes 13 are heated to a temperature sufficiently high, and for a period of time long enough to dry and burn out the binder in the coating on the lower end portion of each exhaust tube and to partially sinter or bind the powder particles of the coating onto the walls of the exhaust tube. To this end, the lower end portions of the exhaust tubes are heated to a temperature just below the point at which they will soften and distort by gas fires 105 (Fig. 8) which are directed by opposed gas burners 10-6 against opposite sides of the coated lower end portions of the tubes during their travel through the heating zone. For example, in the case of soft lead or lime glasses such as are ordinarily used for lamp exhaust tubes and having a melting point of around 650 C., the exhaust tubes 13 should be heated to a temperature of the order of 600 to 650 C. at which temperature the binder will be burned out of the coating on the exhaust tubes and the powder particles of the coating will be set onto the wall of the tubes. A uniform and firmly adherent powder coating is thereby produced on the interior wall of the exhaust tube which will not flake off during the handling of the tube and during the formation of the stem press and after the lamp has been completed.

After the firing and sintering of the coating material onto the inner walls of the exhaust tubes 13, the tubes are then carried through a cooling zone, either with or without forced air cooling as desired, and thence to the upper side or unloading zone of the turret as indicated in Fig. 2 where the tubes are then progressively lifted out of the tube-receiving grooves 15 of the turret, as by an inclined stationary track (not shown) up which the tubes ride as they are carried along by the turret, and are discharged either directly into a suitable receptacle or into a chute which in turn directs them into such a receptacle. The empty tube-receiving grooves 15 of the turret 1 are then advanced once again to the loading zone of the machine where they are again loaded with exhaust tubes 13 from the tube-loading means 37 in preparation for the start of another cycle of operation of the coating apparatus.

From the above description, it will be apparent that we have provided a novel form of coating apparatus which will operate to automatically produce uniform and firmly adherent coatings of powder material on the inner walls of small diameter tubular members, such as glass lamp exhaust tubes and the like, and extending a predetermined distance inwardly from one end of the tubes. The apparatus, moreover, operates continuously and is capable of producing such coated tubes at a very high rate of speed in excess of 4000 coated tubes per hour, without any loss whatever in coating quality.

Although a preferred embodiment of our invention has been disclosed, it will be understood that the invention is not to be limited to the specific construction and arrangement of parts shown, but that they may be widely modified within the spirit and scope of our invention as defined by the appended claims.

What we claim as new and desire to secure by United States Letters Patent is:

1. Apparatus for applying a uniform and firmly adherent coating of powdered material to the inner wall of small diameter tubes inwardly from one end thereof to a predetermined distance, comprising a turret member mounted for rotation about an axis tilted at an angle to the vertical, a plurality of holder means on said turret spaced around the periphery thereof and adapted to hold the tubes thereon in positions tilted radially inward of the turret at an angle to its axis approximately corresponding to the angle of tilt thereof so as to position the tubes approximately vertical when located at the lowermost point in their path of travel around the turret, means for rotating the turret, a dip tank located at the lower side of said turret and containing a suspension of the powdered material into which the tubes are submerged to a predetermined depth during their travel around the turret, and heating means located adjacent the path of travel of said holder means for heating the coated ends of the tubes and baking the coating material thereon.

2. Apparatus as specified in claim 1 wherein the axis of rotation of the said turret is tilted at an angle of approximately 45 to the vertical and the said holder means are adapted to hold the respective tubes in a position tilted radially inward of the turret at an angle to its axis of approximately 45 3. Apparatus for applying a uniform and'firmly adherent coating of powdered material to the inner wall of small diameter tubes inwardly from one end thereof to a predetermined distance, comprising a turret member mounted for rotation about an axis tilted at an angle to the vertical, a plurality of holder means on said turret spaced around the periphery thereof and adapted to hold the tubes thereon in positions tilted radially inward of the turret at an angle to its axis approximately corresponding to the angle of tilt thereof so as to position the tubes approximately vertical when located at the lowermost point in their path of travel around the turret, means for rotating the turret, a dip tank located at the lower side of said turret and containing a suspension of the powdered material into which the tubes are submerged to a predetermined depth during their travel around the turret, air drying means adjacent the path of travel of the holder means from said dip tank for directing heated air down wardly through and against the coated lower ends of the tubes to dry the coating material thereon, brush means mounted adjacent the path of travel of said holder means from said air-drying means for engaging and brushing off the coating from the lower ends and outer sides of the tubes, and heating means located adjacent the path of travel of said holder means from said brushing means for heating the coated ends of the tubes and baking the coating material thereon.

4. Apparatus as specified in claim 3 and comprising, in addition, heating means mounted adjacent the path of travel of said holder means for heating and glazing the upper ends of the tubes held in said holder means.

5. Apparatus for applying a uniform and firmly adherent coating of powdered material to the inner wall of small diameter tubes inwardly from one end thereof to a predetermined distance, comprising a turret member mounted for rotation about an axis tilted at an angle of approximately 45 to the vertical, means for rotating the said turret, the said turret having a beveled upper periphery inclined radially inward of the turret at an angle of approximately 45 and provided with a plurality of grooves extending radially inward of the turret for receiving and supporting individual one of the said tubes in an inclined position corresponding to the inclination of said beveled periphery, said turret having suction ports in its beveled periphery for supplying a vacuum within each of said grooves to hold the tubes in place therein, rotary valve means continuously connecting each of said suction ports to a supply of vacuum, a dip tank located at the lower side of said turret and containing a suspension of the powdered material into which the tubes are submerged to a predetermined depth during their travel around the turret, and heating means located adjacent the path of travel of said holder means for heating the coated ends of the tubes and baking the coating material thereon.

6. Apparatus as specified in claim 5 wherein the said rotary valve means comprises a stationary valve member 1 t having an annular surface of contact with one side of said turret and provided with a plurality of vacuum supply ports located in said contact surface and connected to a source of vacuum, said turret being provided with a plurality of separate manifold chambers each communicating with a respective group of said suction ports in the turret periphery and each having a vacuum inlet port located in the saidcontact side of the turret in position to align and continuously communicate with the said vacuum supply ports in succession during the rotational move- 10 9, 3

merit of the turret.

l2 7. Apparatus as specified in claim 3 wherein the said dip tank comprises a vertically reciprocable troughshaped dipper bowed in a horizontal plane to conform in general with the path of travel of the lower ends of the 5 exhaust tubes therethrough.

References Cited in the file of this patent UNITED STATES PATENTS Laidig et a1 Sept. 21, 1948 2,692,209 Binder Oct. 19, 1954 

